It is common practice in water and/or wastewater filter systems to employ a rotary agitator or sweep adjacent the upper surface of a particulate filter bed, to assist in the cleaning of the filter bed during a backwashing operation. Prior art agitators known to applicant include a rotary arm disposed in a horizontal plane and being connected to a central bearing assembly through a separate coupling member independent of the bearing assembly.
In one prior art device the coupling member is a T-shaped coupler having a pair of axially aligned passages for receiving separate pipe sections that form the arm of the agitator, and a third passage substantially perpendicular to the axially aligned passages for receiving a hollow, tubular member constituting an internal rotor of the central bearing assembly. This prior art arrangement requires the use of an excessive number of parts, and is relatively expensive to fabricate, particularly if one desires to construct the principal components of the agitator, e.g., the arm, the coupler and the bearing assembly, out of stainless steel components. In particular, this prior art arrangement requires the use of two pipe sections to form the arm, a separate coupler to permit the two pipe sections to be connected to the bearing assembly, and a separate bearing assembly interconnected to the coupler. Moreover, the machining operations required to provide the necessary threaded sections for connecting the components of the agitator together undesirably increase manufacturing costs.
In another prior art construction a single, elongate stainless steel pipe section is employed to form the arm of the agitator. In this construction a central, substantially circular opening is machined through the peripheral wall of the pipe, at the midpoint thereof, to communicate with the internal passage extending axially through the pipe section. A stainless steel tubular coupling is welded, about its external surface, to the elongate pipe section in surrounding relationship to the machined opening through the peripheral wall of said pipe section, and this stainless steel coupling receives a descending plastic pipe nipple forming part of the internal rotor of a plastic center bearing assembly.
Securing the internal plastic pipe nipple of the center bearing assembly to the tubular coupling provides a restricted throat, which can become the primary limiting orifice for the flow of fluid through the agitator. Thus it is desirable to enlarge the throat dimension, beyond that which has been achievable in prior art constructions employing a tubular connector secured to a single, elongate pipe section forming the arm or the agitator.